Invaders or saviors? A scholar considers.

In his vivid and illuminating new book, "God's Crucible: Islam and the Making of Europe, 570-1215" (Norton, $29.95), historian David Levering Lewis re-examines the 400-year era of Muslim rule in Europe, a period during which a sophisticated and tolerant Islamic empire conquered - and profoundly influenced - parts of a West that had fallen into barbaric tribalism following the collapse of the Roman empire.

Lewis, a professor at New York University, received the Pulitzer Prize for both volumes of his two-part biography of W.E.B. Du Bois and is the author of eight other books, including "King: A Critical Biography" and "When Harlem Was in Vogue." He spoke from his home in New York City.

Q: What drew you to this period?

A: In a previous book, "The Race to Fashoda," I wrote about the speed bump that the British empire encountered with Islamic fundamentalism in the 1890s. For 10 years the world's mightiest empire was simply stymied in the Upper Sudan. Well, I'm a citizen of the American empire, and I began to see that we were headed for similar speed bumps. I thought it would be useful to write a book - a short book - about Islam in Europe. So off my wife and I went to Morocco, and we arrived in Rabat on the morning of 9/11. A meditation of a time long ago suddenly seemed very pertinent.

Q: It was going to be a short book?

A: But that's not what happened. The post-9/11 culture made it more and more difficult not to write a larger book in which the inferences about then and now would be clearer. I wanted to connect the Iberian history, which is I think fairly well known, with what it meant on the other side of the Pyrenees in terms of the geopolitics and ideology of the Catholic faith. So I spent a lot of time tracing the bargains that arose between these Germans and the bishops of Rome.

Q: Was Europe, in a sense, created by Islam as much as by Christianity?

A: Cautiously I would say yes, and that's what I wanted to emphasize. The Renaissance is profoundly indebted to what I call the conveyor belt of knowledge coming out of Toledo. We would all applaud that, the maintenance and enrichment of the knowledge of Plato and Aristotle, the science of the academy of Athens, the Hindu [mathematics]. In the negative sense, Islam also becomes the template against which Europe compares itself, fights, profits. Finally, the kind of theocracy that emerges in Europe is directly a consequence of Charles Martel's victory over Islam at the Battle of Poitiers in 732.

Q: What if that battle had gone differently?

A: I honestly am impartial about this, but I think the following argument is a fair one based on what happened elsewhere: That if the heartland of what becomes Europe had been incorporated in the Islamic empire, then it would have profited from the commercial, economic, technological, cultural levels of achievement of the Muslims. Europe would have been spared three or four centuries of its laborious, fratricidal, and economically retarded development. Muslim victory would have also meant that the historian Edward Gibbon would have been right when he wrote that "the interpretation of the Koran would now be taught in the schools of Oxford." Well, so what? The wars of religion are right around the corner in Europe, so there you are.

Q: What do you think will most surprise the general reader here?

A: That's always dicey. I tried not to overdo the period of pluralistic collaboration, but it is real. . . . What may also surprise readers is the way in which Charlemagne transformed the Christian faith into a holy war, which, unlike the Muslim jihad, was totally intolerant. In the Islamic empire, much like the Roman empire, as long as you paid your taxes you were pretty much left alone. But with the Carolingians, the Europeans, the Franks, that is not an option. So otherness becomes embedded in European culture in a way that never obtained in Islam and perhaps only today is beginning to be characteristic of that faith.

Q: You write about Karbala, Baghdad, Kufa, and so on. How does it feel when you hear those place names in the news today?

A: It's hard to put into words what goes through your mind, particularly about sites like Ctesiphon, the great palace complex outside Baghdad. In the first Gulf War, as I understand it, the [US] Air Force just barely missed taking it down and now there's an airbase nearby. If these places are wiped out, it's a great pity.

Q: Are you concerned that your book will be viewed as supporting the "clash of civilizations" theory?

A: That would be a gross misreading of the book and certainly not my design. The eschatological simplifiers, supporting that theory, say "Don't you realize where we're going?" I believe that these things have become self-fulfilling prophecies. We are now where we knew we would come to if we did all the worst things and the wrong things. Once people are invaded, polarities are inescapable.